This invention relates to a semiconductor device and a process for producing the same. More particularly, it relates to the technology of semiconductor device fabrication for ensuring that elements formed in an integrated circuit on a semiconductor chip will not break down electrically due to processing steps such as sand blasting and dry etching. The semiconductor device contemplated by the invention is formed as the recording head of ink-jet printer.
A typical process for producing the recording head of a thermal ink-jet printer comprises the steps of preparing a semiconductor device by forming heaters (heat-generating resistors) and their drive circuit on a semiconductor chip (substrate), forming an ink channel and ink supply holes and forming a cavity on each heater that serves as an ink chamber, attaching an orifice plate to the entire surface of the semiconductor device, and opening ink ejection orifices (nozzles) in a position corresponding to each heater.
Conventionally, ink channels and ink supply holes are formed by anisotropic etching of a semiconductor chip with a liquid etchant such as hydrazine or potassium hydroxide (KOH), with the regions other than the ink channels and ink supply holes being masked with a photoresist. However, hydrazine is a very strong carcinogen and has a potential hazard of explosion; KOH is such a strong etchant that it can potentially strip the resist and damage the areas other than the ink channels and ink supply holes.
Alternative methods of forming ink channels and ink supply holes are laser ablation and sand blasting. In sand blasting, small-diameter particles of a blasting medium such as alumina are blown at high speed against a semiconductor device (substrate), with the regions other than ink channels and ink supply holes being masked, to form ink channels and ink supply holes simultaneously in a plurality of semiconductor chips formed on a semiconductor wafer. Sand blasting has the advantage of forming ink channels and ink supply holes in higher resolution with better efficiency than laser ablation.
However, the sand blasting process involving the blowing of small-diameter particles with dry air is not without problems. On account of the friction between the particles and the air, static electricity is generated and the resulting static buildup on the surface of the semiconductor chip can potentially break down the semiconductor device. In the case of the recording head of a thermal ink-jet printer, the drive circuit formed as an element of an integrated circuit on the semiconductor chip may break down due to static buildup during production.
Speaking further of the recording head of a thermal ink-jet printer, orifices are usually formed by dry etching an orifice plate while masking the regions other than those corresponding to the individual heaters. However, when orifices are opened by dry etching, molecules in the state of an ion plasma cause static buildup on the oxidized film formed on each heater and can potentially break down the drive circuit connected to each heater.
The present invention has been accomplished under these circumstances and has an object providing a semiconductor device furnished with a structure which ensures that elements that comprise a drive circuit for driving an ink ejection or delivery unit and which are formed in an integrated circuit on a semiconductor chip to comprise the recording head of an ink-jet printer will not break down electrically during fabrication due to processing steps such as sand blasting and dry etching.
Another object of the invention is to provide a process for producing the semiconductor device.
The first object of the invention can be attained by a semiconductor device according to its first aspect which is in the form of a semiconductor chip formed as a recording head of an ink-jet printer, the semiconductor chip comprising at least an ink ejection unit, an integrated circuit composed of a drive circuit for driving the ink ejection unit, bonding pads and a metal film covering at least part of an upper layer of the integrated circuit, the metal film being formed to extend from the integrated circuit to an edge of the semiconductor chip.
Preferably, the metal film also covers further an upper layer of at least one of the bonding pads in such a way as to extend from the bonding pad to an edge of the semiconductor chip.
According to its first aspect, the invention also provides a semiconductor device as a semiconductor wafer including at least two semiconductor chips of the structure described above and at least one grounding pad being formed of the metal film in a region peripheral to the semiconductor wafer and which is outside the semiconductor chips, wherein the metal film is also formed in a region between the semiconductor chips, and wherein the metal films formed to extend to edges of all the semiconductor chips are interconnected via the region between the semiconductor chips and also connected to the grounding pad.
Preferably, the region between the semiconductor chips is a scribing line.
In each of the embodiments described above, the ink ejection unit includes heat-generating resistors, the metal film is formed of the same material as the heat-generating resistors, and the recording head of the ink-jet printer is a recording head of a thermal ink-jet printer.
The second object of the invention can be attained by a process according to its second aspect for producing a semiconductor device in a semiconductor wafer having at least two semiconductor chips formed thereon, each serving as a recording head of an ink-jet printer, which process comprises the steps of forming at least an ink ejection unit and an integrated circuit composed of a drive circuit for driving the ink ejection unit on a semiconductor substrate for each of the semiconductor chips, covering at least part of an upper layer of the integrated circuit on each of the semiconductor chips to form metal films that each extend from the integrated circuit to an edge of each of the corresponding semiconductor chips and which are also interconnected via a region between the semiconductor chips, and also forming at least one grounding pad from the metal film in a region peripheral to the semiconductor wafer and which is outside the semiconductor chips, the grounding pad being connected to the metal film via the region between the semiconductor chips, and applying a processing step with the metal films being grounded via the grounding pad.
Preferably, the ink ejection unit includes the heat-generating resistors, the recording head of the ink-jet printer is a recording head of a thermal ink-jet printer, and the metal films are formed of the same material as the heat-generating resistors simultaneously with formation of the heat-generating resistors after forming the drive circuit.
Preferably, not only the integrated circuit but also bonding pads are further formed on the semiconductor substrate for each of the semiconductor chips, and the metal film also covers further an upper layer of at least one of the bonding pads in such a way as to extend from the bonding pad to an edge of each of the semiconductor chips.
Preferably, the processing step is either a step of forming an ink channel for supplying ink to each of the ink ejection unit or a step of boring ink supply holes through each of the semiconductor substrate for supplying ink to the ink channel or both steps.
Preferably, the region between the semiconductor chips is a scribing line.
Preferably, the metal films are also further formed on a reverse side of the semiconductor wafer which is opposite a side where the integrated circuits for the semiconductor chips are formed.
Preferably, the metal films formed on the reverse side of the semiconductor wafer cover the entire surface of the reverse side of the semiconductor wafer.
Preferably, the metal films formed on the reverse side of the semiconductor wafer are removed after finishing of the processing step.